Phase change memory cell having vertical channel access transistor

ABSTRACT

A device includes a substrate having a first region and a second region. The first region comprises a first field effect transistor having a horizontal channel region within the substrate, a gate overlying the horizontal channel region, and a first dielectric covering the gate of the first field effect transistor. The second region of the substrate includes a second field effect transistor comprising a first terminal extending through the first dielectric to contact the substrate, a second terminal overlying the first terminal and having a top surface, and a vertical channel region separating the first and second terminals. The second field effect transistor also includes a gate on the first dielectric and adjacent the vertical channel region, the gate having a top surface that is co-planar with the top surface of the second terminal.

RELATED APPLICATIONS

This application is a continuation application of co-pending U.S. patentapplication Ser. No. 13/110,197 filed on 18 May 2011, which applicationis a divisional application of U.S. patent application Ser. No.12/471,301 filed on 22 May 2009 (now U.S. Pat. No. 7,968,876).

PARTIES TO A JOINT RESEARCH AGREEMENT

International Business Machines Corporation, a New York Corporation, andMacronix International Corporation, Ltd., a Taiwan corporation, areparties to a Joint Research Agreement.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to high density memory devices based onphase change memory materials, including chalcogenide based materialsand on other programmable resistance materials, and methods formanufacturing such devices.

2. Description of Related Art

Phase change based memory materials, like chalcogenide based materialsand similar materials, can be caused to change phase between anamorphous state and a crystalline state by application of electricalcurrent at levels suitable for implementation in integrated circuits.The generally amorphous state is characterized by higher electricalresistivity than the generally crystalline state, which can be readilysensed to indicate data. These properties have generated interest inusing programmable resistance material to form nonvolatile memorycircuits, which can be read and written with random access.

The change from the amorphous to the crystalline state is generally alower current operation. The change from crystalline to amorphous,referred to as reset herein, is generally a higher current operation,which includes a short high current density pulse to melt or breakdownthe crystalline structure, after which the phase change material coolsquickly, quenching the molten phase change material and allowing atleast a portion of the phase change material to stabilize in theamorphous state.

The magnitude of the current needed for reset can be reduced by reducingthe size of the phase change material element in the cell and/or thecontact area between electrodes and the phase change material, so thathigher current densities are achieved with small absolute current valuesthrough the phase change material.

One approach to reducing the size of the phase change element in amemory cell is to form small phase change elements by etching a layer ofphase change material. However, reducing the size of the phase changeelement by etching can result in damage to the phase change material dueto non-uniform reactivity with the etchants which can cause theformation of voids, compositional and bonding variations, and theformation of nonvolatile by-products. This damage can result invariations in shape and uniformity of the phase change elements acrossan array of memory cells, resulting in electrical and mechanicalperformance issues for the cell.

Additionally, it is desirable to reduce the cross-sectional area orfootprint of individual memory cells in an array of memory cells inorder to achieve higher density memory devices. However, traditionalfield effect transistor access devices are horizontal structures havinga horizontally oriented gate overlying a horizontally oriented channelregion, resulting in the field effect transistors having a relativelylarge cross-sectional area which limits the density of the array.Attempts at reducing the cross-sectional area of horizontally orientedfield effect transistors can result in issues in obtaining the currentneeded to induce phase change because of the relatively low currentdrive of field effect transistors.

Thus, memory devices including both vertically and horizontally orientedfield effect transistors have been proposed. See, for example, U.S. Pat.No. 7,116,593. However, the integration of both vertically andhorizontally oriented field effect transistors can be difficult andincrease the complexity of designs and manufacturing processes. Thus,issues that devices having both vertically and horizontally orientedfield effect transistors need to address include cost and simplicity ofmanufacturing.

Although bipolar junction transistors and diodes can provide a largercurrent drive than field effect transistors, it can be difficult tocontrol the current in the memory cell using a bipolar junctiontransistor or a diode adequately enough to allow for multi-bitoperation. Additionally, the integration of bipolar junction transistorswith CMOS periphery circuitry is difficult and may result in highlycomplex designs and manufacturing processes.

It is therefore desirable to provide both vertically and horizontallyoriented field effect transistors on the same substrate that are readilymanufactured for use in high-density memory devices, as well as in otherdevices that may have a need for both types of transistors on one chip.It is also desirable to provide memory devices providing the currentnecessary to induce phase change, as well as addressing the etchingdamage problems described above.

SUMMARY OF THE INVENTION

Devices having both vertically and horizontally oriented field effecttransistors are described along with methods for manufacturing. A deviceas described herein includes a substrate having a first region and asecond region. The first region includes a first field effect transistorcomprising first and second doped regions separated by a horizontalchannel region within the substrate. A gate of the first field effecttransistor overlies the horizontal channel region, and a firstdielectric covers the gate. The second region of the substrate includesa second field effect transistor comprising a first terminal extendingthrough the first dielectric to contact the substrate, a second terminaloverlying the first terminal and having a top surface, and a verticalchannel region separating the first and second terminals. A gate of thesecond field effect transistor is on the first dielectric and adjacentthe vertical channel region, the gate having a top surface that isco-planar with the top surface of the second terminal. A seconddielectric separates the gate of the second field effect transistor fromthe vertical channel region.

In embodiments the device is a memory device in which the first regionis a periphery region and the second region is a memory region, and thesecond region further comprises a programmable resistance memory elementelectrically coupled to the second terminal of the field effecttransistor.

In embodiments the second region further comprises a plurality of wordlines on the first dielectric, and an array comprising a plurality offield effect transistors including the second field effect transistor,the gate of the second field effect transistor coupled to acorresponding word line in the plurality of word lines.

In embodiments described herein the second terminals of the transistorsand the word lines are both planarized using a planarization process,such as CMP, so that the top surfaces of the second terminals and theword lines are co-planar. Additionally, a silicide process can then beperformed to form both conductive caps comprising silicide on the topsurfaces of the second terminals, and conductive layers comprisingsilicide on the top surfaces of the word lines at the same time.

In embodiments the vertical field effect transistors can be formedwithin the corresponding word line such that the allocatedcross-sectional area of memory cells in an array can be determinedentirely by dimensions of the word lines and bit lines, allowing for ahigh memory density of the array.

The channel region and the first and second terminals are arrangedvertically so that the field effect transistor can have a smallcross-sectional area while also providing sufficient current to inducephase change. The length of the channel of the device is determined bythe height of the channel region and can made small, while the width ofthe channel of the device is dependent upon the circumference of thechannel region and can be made relatively large compared to the length.Thus, a relatively large width-to-length ratio can be achieved such thathigher reset current can be obtained.

A method for manufacturing a device as described herein comprisesforming a substrate and forming a first dielectric on the substrate. Aplurality of openings are formed in the first dielectric to exposeportions of the substrate. First and second terminals and channelregions of respective field effect transistors are formed withincorresponding openings in the plurality of openings, the first terminalscontacting the substrate. A portion of the first dielectric is removedto expose outer surfaces of the channel regions, and a second dielectricis formed on the exposed outer surfaces of the channel regions. Wordlinematerial is formed on remaining portions of the first dielectric andsurrounding the second dielectric, and the word line material ispatterned to form a plurality of word lines. Programmable resistancememory material is formed electrically coupled to the second terminalsof the field effect transistors, and conductive material is formed onthe programmable resistance memory material.

Also, in embodiments described herein logic devices in the peripheryregion and memory cells having vertical channel transistors aremanufactured concurrently. The first terminals of the transistors of thememory cells and the gate dielectric of logic devices in the peripheryregion can both be formed on the top surface of the same substrate.Additionally, the word lines are formed on the material from thedielectric layer that covers the gate structure of the logic device inthe periphery region. As a result, memory devices described hereininclude vertical channel transistors compatible with CMOS peripherycircuitry and addressing the complexity of design integration andmanufacturing processes.

Other aspects and advantages of the present invention can be seen onreview of the drawings, the detailed description, and the claims whichfollow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic diagram of a potion of a memory cellarray implemented using memory cells having field effect transistorswith vertical channels and memory elements comprising programmableresistance material of a memory plane.

FIGS. 2A-2B illustrate cross-sectional views of a portion of anembodiment of memory cells arranged in the array of FIG. 1.

FIGS. 2C and 2D illustrate cross-sectional views an alternativeembodiment in which the electrodes of the array of FIGS. 2A and 2B areomitted and the memory material of the memory element extends within theopening in the dielectric to contact the conductive cap.

FIGS. 3-11B illustrate steps in a fabrication sequence for manufacturingthe array of memory cells of FIGS. 2A-2B.

FIG. 12 is a simplified block diagram of an integrated circuit includinga memory array implemented using memory cells having a memory planeoverlying vertical channel field effect transistor access devices.

FIG. 13 illustrates a schematic diagram of a portion of a memory cellarray implemented using memory cells having field effect transistorswith vertical channels and memory elements comprising programmableresistance material, the transistors arranged in a common sourceconfiguration.

FIGS. 14A-14B illustrate cross-sectional views of a portion of anembodiment of memory cells arranged in the array of FIG. 13.

FIGS. 15-16B illustrate steps in a fabrication sequence formanufacturing the array of memory cells of FIGS. 14A-14B.

FIG. 17 is a simplified block diagram of an integrated circuit includinga memory array implemented using memory cells vertical channel fieldeffect transistor access devices arranged in a common sourceconfiguration.

DETAILED DESCRIPTION

The following description of the disclosure will typically be withreference to specific structural embodiments and methods. It is to beunderstood that there is no intention to limit the disclosure to thespecifically disclosed embodiments and methods, but that the disclosuremay be practiced using other features, elements, methods andembodiments. Preferred embodiments are described to illustrate thepresent disclosure, not to limit its scope, which is defined by theclaims. Those of ordinary skill in the art will recognize a variety ofequivalent variations on the description that follows. Like elements invarious embodiments are commonly referred to with like referencenumerals.

FIG. 1 illustrates a schematic diagram of a portion of a memory cellarray 100 implemented using memory cells having field effect transistorswith vertical channels and memory elements comprising programmableresistance material of a memory plane as described herein.

As shown in the schematic diagram of FIG. 1, each of the memory cells ofarray 100 includes a field effect transistor access device and a memoryelement arranged in electrical series, the memory elements capable ofbeing set to one of a plurality of resistive states and thus capable ofstoring one or more bits of data.

The array 100 comprises a plurality of bit lines 120 including bit lines120 a, 120 b, 120 c, 120 d extending in parallel in a first directionand in electrical communication with bit line decoder 160. The fieldeffect transistors of the array 100 have first terminals acting as asource or drain coupled to a corresponding bit line 120.

A plurality of word lines 130 including word lines 130 a, 130 b, 130 c,130 d extend in parallel in a second direction and are in electricalcommunication with word line decoder/driver 150. As described in moredetail below with respect to FIGS. 2A-2B, the word lines 130 overly thebit lines 120. The word lines 130 are adjacent to the vertical channelsof the field effect transistors to act as the gate terminals of thetransistors. In alternative embodiments, the word lines 130 maycompletely or partially surround the channels, or otherwise lie adjacentthe channels, and are separated from the channels by a gate dielectriclayer.

The memory elements of the memory cells of array 100 comprise respectiveportions of the programmable resistance memory material of a memoryplane (described in more detail below with respect to FIGS. 2A-2B)overlying the bit lines 130 and word lines 120 of the array 100. Thememory elements of the memory cells are electrically coupled to thesecond terminals of the field effect transistors by electrodes 250 thatprovide a small contact area between the field effect transistors andthe memory elements.

The memory plane includes conductive material 140 (described in moredetail below with respect to FIGS. 2A-2B) on the programmable resistancememory material. The conductive material 140 of the memory plane iselectrically coupled to a memory plane termination circuit 170. In theillustrated embodiment the memory plane termination circuit 170 is aground terminal, but may alternatively include a voltage source forapplying a common voltage other than ground to the conductive materialof the memory plane.

Memory cell 110 is representative of memory cells of array 100 andcomprises field effect transistor 115 and phase change memory element125 arranged electrically in series between the memory plane and thecorresponding bit lines 120. The word line 130 b acts as the gateterminal of the transistor 115, and the first terminal (acting as thesource or drain of the transistor 115) is coupled to bit line 120 b. Thememory element 125, comprising programmable resistance memory materialof the memory plane overlying the word lines 130 and bit lines 120, iselectrically coupled between the second terminal of the transistor 125and the conductive material 140 of the memory plane.

Reading or writing to memory cell 110 of array 100 can be achieved byapplying an appropriate voltage to the corresponding word line 130 b andan appropriate voltage or current the corresponding bit line 120 b toinduce a current through the memory element 125. The level and durationof the voltages/currents applied is dependent upon the operationperformed, e.g. a reading operation or a writing operation.

In a reset (erase) operation of the memory cell 110, a reset pulseapplied to the word line 130 b and the bit line 120 b induces a currentthrough the memory element 125 to cause a transition of an active regionof the memory element 125 into an amorphous phase, thereby setting thephase change material to a resistance within a resistive value rangeassociated with the reset state. The reset pulse is a relatively highenergy pulse, sufficient to raise the temperature of at least the activeregion of the memory element 125 above the transition (crystallization)temperature of the phase change material and also above the meltingtemperature to place at least the active region in a liquid state. Thereset pulse is then quickly terminated, resulting in a relatively quickquenching time as the active region quickly cools to below thetransition temperature so that the active region stabilizes to agenerally amorphous phase.

In a set (or program) operation of memory cell 110, a program pulse isapplied to the word line 130 b and the bit line 120 b of suitableamplitude and duration to induce a current through the memory element125 sufficient to raise the temperature of at least a portion of theactive region of the memory element 125 above the transition temperatureand cause a transition of at least a portion of the active region fromthe amorphous phase into a crystalline phase, this transition loweringthe resistance of the memory element 125 and setting the memory cell 110to the desired state.

In a read (or sense) operation of the data value stored in the memorycell 110, a read pulse applied to the corresponding word line 130 b andthe corresponding bit line 120 b of suitable amplitude and duration toinduce current to flow through the memory element 125 that does notresult in the memory element 125 undergoing a change in resistive state.The current through the memory cell 110 is dependent upon the resistanceof the memory element 125 and thus the data value stored in the memorycell 110. The data valued stored in the memory cell 110 may bedetermined, for example, by comparison of the current on bit line 120 bwith a suitable reference current by sense amplifiers of block 165.Alternatively, the data value stored in the memory cell 110 may bedetermined, for example, using source side sensing by comparison of thecurrent on the conductive material 140 of the memory plane with asuitable reference current.

FIGS. 2A and 2B illustrate cross-sectional views of a portion of anembodiment of memory cells (including representative memory cell 110)arranged in the array 100, FIG. 2A taken along the word lines 130 andFIG. 2B taken along the bit lines 120.

The array 100 includes a memory region 1900 and periphery region 1910 onthe single-crystalline semiconductor substrate 200. The substrate 200has a substantially planar top surface 201. As used herein, the term“substantially planar” is intended to accommodate manufacturingtolerances during the formation of the substrate 200. The term“substantially planar” is also intended to accommodate manufacturingprocesses performed following the formation of the substrate 200 whichmay cause variations in the planarity of the top surface 201.

The periphery region 1910 includes logic device 1986 having a gatestructure 1987 on a gate dielectric layer 1993. The gate dielectriclayer 1993 is on the top surface 201 of the substrate 200. The gatestructure 1987 comprises a layer of doped polysilicon on the gatedielectric layer 1993, and a layer of silicide on the doped polysilicon.

The logic device 1986 includes doped regions 1988, 1989 within thesubstrate 200 acting as the source and drain regions. A dielectric 1996comprising one or more layers of dielectric material is on the logicdevice 1986.

Contact 1965 is coupled to doped region 1989 and extends to the topsurface of dielectric 1996 to line 1960. Contact 1995 is coupled to thedoped region 1988 and extends to the top surface of dielectric 1996 toline 1997. The line 1997 extends into memory region 1900 and is coupledto the conductive material 140 of the memory plane 295 by contact 1950extending through dielectric 1996.

The array 100 includes a single-crystalline substrate 200 comprising awell 205 having a first conductivity type and bit lines 120 within thewell 205. The bit lines 120 extend in a first direction into out of thecross-section illustrated in FIG. 2A and are separated by dielectrictrench isolation structures 232 within the well 205. The bit lines 120comprise doped substrate material having a second conductivity typeopposite that of the first conductivity type. In the illustratedembodiment the doped substrate material of the bit lines 120 compriseshigh doped N-type (N+) material of the substrate 200, and the well 205comprise doped P-type material of the substrate 200.

The field effect transistor 115 of the memory cell 110 includes a firstterminal 122 comprising doped semiconductor material on thecorresponding bit line 120 b, a channel region 123 comprising dopedsemiconductor material on the first terminal 122, and a second terminal124 comprising doped semiconductor material on the channel region 123.

A conductive cap 127 comprising silicide is on the second terminal 124.The conductive cap 127 may comprise, for example, a silicide containingTi, W, Co, Ni, or Ta. The conductive cap 127 provides a low resistancecontact between the doped semiconductor material 126 and an electrode250.

In the illustrated embodiment the first and second terminals 122, 124comprise highly doped N-type material, and the channel region 123comprises doped P-type material.

The first and second terminals 122, 124, the channel region 123, and theconductive cap 127 form a stack which is surrounded by a dielectric 230,the dielectric 230 separating the channel region 123 from thecorresponding word line 130 b.

The word lines 130, include word line 130 b acting as the gate of thefield effect transistor 115 of the memory cell 110, extend into and outof the cross section illustrated in FIG. 2B and comprise dopedpolysilicon material and a silicide layer on the doped polysilicon. Thestack formed by the first and second terminals 122, 124, the channelregion 123, and the conductive cap 127 extends through a via in the wordline 130 b to electrically couple the bit line 120 b to the electrode250, the via in the word line 130 b having a sidewall surface 135surrounding the channel region 123.

The electrode 250 is on the conductive cap 127 and extends throughdielectric 270 to a memory element 125 comprising a portion of theprogrammable resistance memory material 290 of memory plane 295. Theprogrammable resistance memory material may comprise, for example, oneor more elements from the group of Ge, Sb, Te, Se, In, Ti, Ga, Bi, Sn,Cu, Pd, Pb, Ag, S, Si, 0, P, As, N and Au.

The electrode 250 may comprise, for example, TiN or TaN. TiN may bepreferred in embodiments in which memory material 290 comprises GST(discussed in more detail below) because it makes good contact with GST,it is a common material used in semiconductor manufacturing, and itprovides a good diffusion barrier at the higher temperatures at whichGST transitions, typically in the 600-700° C. range. Alternatively, theelectrode 250 may comprise, for example, one or more elements from thegroup of Ti, W, Mo, Al, Ta, Cu, Pt, Ir, La, Ni, N, O, and Ru.

The conductive material 140 of the memory plane 295 is on theprogrammable resistance memory material 290 and is coupled to a commonvoltage. In embodiments the conductive material 140 may comprise one ormore conductive layers each comprising, for example, one or moreelements from the group of Ti, W, Mo, Al, Ta, Cu, Pt, Ir, La, Ni, N, O,and Ru. Advantages of having at least two conductive layers for theconductive material 140 include choosing the material of a firstconductive layer for compatibility with the memory material 290 of thememory plane 295, while material of a second conductive layer on thefirst conductive layer can be chosen for other advantages such as higherelectrical conductivity than the first conductive layer.

In operation, the common voltage coupled to the conductive material 140and voltages supplied to the word line 130 b and the bit line 120 b caninduce current to flow from the bit line 120 b to the conductivematerial 140, or vice versa, via the first terminal 122, channel region123, second terminal 124, conductive cap 127, electrode 250, and memorymaterial 290.

The active region 128 is the region of the memory element 125 in whichthe memory material is induced to change between at least two solidphases. As can be appreciated, the active region 128 can be madeextremely small in the illustrated structure, thus reducing themagnitude of current needed to induce a phase change. The thickness 292of the memory material 290 can be established using thin film depositiontechniques. In some embodiments the thickness 292 is less than 100 nm,for example being between 10 and 100 nm. Furthermore, the electrode 250has a width 252 less than that of the conductive cap 127, and preferablyless than a minimum feature size for a process, typically a lithographicprocess, used to form the word lines 130 of the array 100. Thus, theelectrode 250 has a top surface contacting the memory material 290 ofthe memory plane 295, the top surface of the electrode 250 having asurface area less than the top surface of the conductive cap 127. Thesmall top surface of the electrode 250 concentrates current density inthe portion of the memory plane 290 adjacent the electrode 250, therebyreducing the magnitude of the current needed to induce a phase change inthe active region 128. Additionally, the dielectric 270 may provide somethermal isolation to the active region 128, which also helps to reducethe amount of current necessary to induce a phase change.

As can be seen in FIGS. 2A and 2B, the first terminals 122 of the accesstransistors in the memory region 1910 and the gate dielectric layer 1993are both on the substantially planar top surface 201 of the substrate.As described in more detail below with reference to FIGS. 3 to 11, thelogic device 1986 in the periphery region and the memory cells havingvertical channels can be manufactured concurrently. As a result, thememory device has a reduced complexity and addresses design integrationissues of periphery and memory regions, thereby reducing the cost.

In FIGS. 2A-2B, the active region 128 has a “mushroom” shape, and thusthe configuration of the electrode 250 and the memory element 125 iscommonly referred to as a mushroom-type configuration. Alternatively,other types of configurations can be used.

FIGS. 2C and 2D illustrate cross-sectional views an alternativeembodiment in which the electrodes 250 of the array of FIGS. 2A and 2Bare omitted and the memory material 290 of the memory element 125extends within the opening in the dielectric 270 to contact theconductive cap 127, resulting in a pore-type cell.

In the cross-sectional views of FIGS. 2A-2B the programmable resistancememory material 290 is a blanket layer of programmable resistance memorymaterial extending across to contacting the electrodes 250 of the memorycells of the array 100, and thus the array 100 is not subject to theetching damage problems discussed above. In FIGS. 2A-2B the conductivematerial 140 comprises a blanket layer of conductive material on theblanket layer of programmable resistance memory material. In someembodiments the memory material 290 and the conductive material 140 maybe patterned, for example, to form patches, strips or grids, theformation of patches, strips or grids removing memory material that isspaced away from the active regions so that the active regions are notsubject to etch damage.

The channel regions 123 have a top view cross-sectional channel areawhich in the illustrated embodiment is defined by a first dimension 224along a first direction along the word lines 130 as shown in FIG. 2A,and a second dimension 226 along a second direction along the bit lines120 perpendicular to the first direction as shown in FIG. 2B. In someembodiments the memory material 290 may be patterned into a plurality ofmemory patches each having a top view cross-sectional patch area. Thispatch area may be, for example, greater than or equal to ten times thetop view cross-sectional area of the channel regions 123 so that thememory patches are shared among neighboring memory cells and the activeregions are not subject to etch damage.

In yet other embodiments the conductive material 140 may be patterned,for example into strips or a grid structure, while maintaining a blanketlayer of memory material for the memory plane 290.

As can be seen in FIG. 2A, because of the vertical channel structure ofthe field effect transistors the memory cell density along the wordlines 130 b is determined by the width of the bit lines 120 and theseparation distance between adjacent bit lines 120. As can be seen inFIG. 2B, the memory cell density along the bit lines 120 b is determinedby the width of the word lines 130 and the separation distance betweenadjacent word lines 130. Thus, the cross-sectional area of the memorycells of the array 100 is determined entirely by dimensions of the wordlines 130 and bit lines 120, allowing for a high memory density of thearray.

Additionally, since the channel region 123 and the first and secondterminals 122, 126 are arranged vertically the field effect transistorcan have a small cross-sectional area while also providing sufficientcurrent to induce phase change. The length of the channel of the deviceis determined by the height of the channel region 123 and can madesmall, while the width of the channel of the device is dependent uponthe circumference of the channel region 123 and can be made relativelylarge compared to the length. Thus, a relatively large width-to-lengthratio can be achieved such that higher reset current can be obtained.

Embodiments of the programmable resistance material 290 of the memoryplane include phase change based memory materials, includingchalcogenide based materials and other materials. Chalcogens include anyof the four elements oxygen (O), sulfur (S), selenium (Se), andtellurium (Te), forming part of group VIA of the periodic table.Chalcogenides comprise compounds of a chalcogen with a moreelectropositive element or radical. Chalcogenide alloys comprisecombinations of chalcogenides with other materials such as transitionmetals. A chalcogenide alloy usually contains one or more elements fromgroup IVA of the periodic table of elements, such as germanium (Ge) andtin (Sn). Often, chalcogenide alloys include combinations including oneor more of antimony (Sb), gallium (Ga), indium (In), and silver (Ag).Many phase change based memory materials have been described intechnical literature, including alloys of: Ga/Sb, In/Sb, In/Se, Sb/Te,Ge/Te, Ge/Sb/Te, In/Sb/Te, Ga/Se/Te, Sn/Sb/Te, In/Sb/Ge, Ag/In/Sb/Te,Ge/Sn/Sb/Te, Ge/Sb/Se/Te and Te/Ge/Sb/S. In the family of Ge/Sb/Tealloys, a wide range of alloy compositions may be workable. Thecompositions can be characterized as Te_(a)Ge_(b)Sb_(100-(a+b)). Oneresearcher has described the most useful alloys as having an averageconcentration of Te in the deposited materials well below 70%, typicallybelow about 60% and ranged in general from as low as about 23% up toabout 58% Te and most preferably about 48% to 58% Te. Concentrations ofGe were above about 5% and ranged from a low of about 8% to about 30%average in the material, remaining generally below 50%. Most preferably,concentrations of Ge ranged from about 8% to about 40%. The remainder ofthe principal constituent elements in this composition was Sb. Thesepercentages are atomic percentages that total 100% of the atoms of theconstituent elements. (Ovshinsky U.S. Pat. No. 5,687,112, cols. 10-11.)Particular alloys evaluated by another researcher include Ge₂Sb₂Te₅,GeSb₂Te₄ and GeSb₄Te₇ (Noboru Yamada, “Potential of Ge—Sb—TePhase-Change Optical Disks for High-Data-Rate Recording”, SPIE v. 3109,pp. 28-37 (1997).) More generally, a transition metal such as chromium(Cr), iron (Fe), nickel (Ni), niobium (Nb), palladium (Pd), platinum(Pt) and mixtures or alloys thereof may be combined with Ge/Sb/Te toform a phase change alloy that has programmable resistance properties.Specific examples of memory materials that may be useful are given inOvshinsky '112 at columns 11-13, which examples are hereby incorporatedby reference.

Chalcogenides and other phase change materials are doped with impuritiesin some embodiments to modify conductivity, transition temperature,melting temperature, and other properties of memory elements using thedoped chalcogenides. Representative impurities used for dopingchalcogenides include nitrogen, silicon, oxygen, silicon dioxide,silicon nitride, copper, silver, gold, aluminum, aluminum oxide,tantalum, tantalum oxide, tantalum nitride, titanium and titanium oxide.See, e.g., U.S. Pat. No. 6,800,504, and U.S. Patent ApplicationPublication No. U.S. 2005/0029502.

Phase change alloys are capable of being switched between a firststructural state in which the material is in a generally amorphous solidphase, and a second structural state in which the material is in agenerally crystalline solid phase in its local order in the activechannel region of the cell. These alloys are at least bistable. The termamorphous is used to refer to a relatively less ordered structure, moredisordered than a single crystal, which has the detectablecharacteristics such as higher electrical resistivity than thecrystalline phase. The term crystalline is used to refer to a relativelymore ordered structure, more ordered than in an amorphous structure,which has detectable characteristics such as lower electricalresistivity than the amorphous phase. Typically, phase change materialsmay be electrically switched between different detectable states oflocal order across the spectrum between completely amorphous andcompletely crystalline states. Other material characteristics affectedby the change between amorphous and crystalline phases include atomicorder, free electron density and activation energy. The material may beswitched either into different solid phases or into mixtures of two ormore solid phases, providing a gray scale between completely amorphousand completely crystalline states. The electrical properties in thematerial may vary accordingly.

Phase change alloys can be changed from one phase state to another byapplication of electrical pulses. It has been observed that a shorter,higher amplitude pulse tends to change the phase change material to agenerally amorphous state. A longer, lower amplitude pulse tends tochange the phase change material to a generally crystalline state. Theenergy in a shorter, higher amplitude pulse is high enough to allow forbonds of the crystalline structure to be broken and short enough toprevent the atoms from realigning into a crystalline state. Appropriateprofiles for pulses can be determined, without undue experimentation,specifically adapted to a particular phase change alloy. In followingsections of the disclosure, the phase change material is referred to asGST, and it will be understood that other types of phase changematerials can be used. A material useful for implementation of a PCRAMdescribed herein is Ge₂Sb₂Te₅.

Other programmable resistance memory materials may be used in otherembodiments of the invention, including other materials that usedifferent crystal phase changes to determine resistance, or other memorymaterials that use an electrical pulse to change the resistance state.Examples include materials for use in resistance random access memory(RRAM) such as metal-oxides including tungsten-oxide (WO_(x)), NiO,Nb₂O₅, CuO₂, Ta₂O₅, Al₂O₃, CoO, Fe₂O₃, HfO₂, TiO₂, SrTiO₃, SrZrO₃,(BaSr)TiO₃. Additional examples include materials for use inmagnetoresistance random access memory (MRAM) such asspin-torque-transfer (STT) MRAM, for example at least one of CoFeB, Fe,Co, Ni, Gd, Dy, CoFe, NiFe, MnAs, MnBi, MnSb, CrO₂, MnOFe₂O₃, FeOFe₂O₅,NiOFe₂O₃, MgOFe₂, EuO, and Y₃Fe₅O₁₂. See, for example, US Publication No2007/0176251 entitled “Magnetic Memory Device and Method of Fabricatingthe Same”, which is incorporated by reference herein. Additionalexamples include solid electrolyte materials used forprogrammable-metallization-cell (PMC) memory, or nano-ionic memory, suchas silver-doped germanium sulfide electrolytes and copper-dopedgermanium sulfide electrolytes. See, for example, N. E. Gilbert et al.,“A macro model of programmable metallization cell devices,” Solid-StateElectronics 49 (2005) 1813-1819, which is incorporated by referenceherein.

An exemplary method for forming chalcogenide material usesPVD-sputtering or magnetron-sputtering method with source gas(es) of Ar,N₂, and/or He, etc. at the pressure of 1 mTorr˜100 mTorr. The depositionis usually done at room temperature. A collimator with an aspect ratioof 1˜5 can be used to improve the fill-in performance. To improve thefill-in performance, a DC bias of several tens of volts to severalhundreds of volts is also used. On the other hand, the combination of DCbias and the collimater can be used simultaneously.

An exemplary method for forming chalcogenide material uses chemicalvapor deposition CVD such as that disclosed in US Publication No2006/0172067 entitled “Chemical Vapor Deposition of ChalcogenideMaterials”, which is incorporated by reference herein.

A post-deposition annealing treatment in a vacuum or in an N₂ ambient isoptionally performed to improve the crystallize state of chalcogenidematerial. The annealing temperature typically ranges from 100° C. to400° C. with an anneal time of less than 30 minutes.

FIGS. 3 to 11 illustrate steps in a fabrication sequence suitable formanufacturing an array of memory cells illustrated in FIGS. 2A-2B.

FIG. 3 illustrates a step including forming a substrate 200 comprising awell 205 and trench isolation structures 232 within the well 205 andextending into and out of the cross-section illustrated in FIG. 20. Thewell 205 can be formed by implantation and activation annealingprocesses as known in the art. In the illustrated embodiment the wellcomprises doped P type material of silicon substrate 200. The substrate200 has top surface 201.

Next, gate dielectric layer 1993 is formed on the top surface 201 of theperiphery region 1910 of the substrate 200 of FIG. 3. Gate structure1987 is formed by depositing and patterning doped polysilicon material,and then forming a conductive cap comprising silicide on the dopedpolysilicon material, resulting in the structure illustrated in thecross-sectional view of FIG. 4. Alternatively, other techniques may beused to form the gate structure 1987.

Next, the bit lines 120 are formed within the well 205 and doped regions1988, 1989 acting as the source and drain are formed within theperiphery region 1910, resulting in the structure illustrated in thecross-sectional view of FIG. 5. In the illustrated embodiment the bitlines 120 and doped regions 1988, 1989 are formed by ion implantation.

Next, dielectric 2300 is formed on the structure illustrated in FIG. 5and a plurality of openings 2310 are formed in the dielectric 2300 toexpose portions of the bit lines 120, resulting in the structureillustrated in FIG. 6. The dielectric 2300 may comprise, for example,boro-phospho-silicate glass (BPSG) or PSG.

Next, a selective epitaxial process is performed within the openings2310 to form doped regions (first terminals) 122 on the bit lines 120,resulting in the structure illustrated in the cross-sectional view ofFIG. 7. In the illustrated embodiment the doped regions 122 compriseN-type doped silicon.

Next, another selective epitaxial process is performed within theopenings and a planarizing process such as CMP is performed to formdoped pillars 2500, resulting in the structure illustrated in thecross-sectional view of FIG. 8. The doped pillars 2500 have aconductivity type opposite that of the doped regions 122, and in theillustrated embodiment comprise P-type doped silicon.

Next, an implantation process is performed to implant dopants within anupper portion of the pillars 2500 to form doped regions (secondterminals) 124 having the same conductivity type as the doped regions122, resulting in the structure illustrated in the cross-sectional viewof FIG. 9. The remaining portions of the pillars 2500 between the dopedregions 122 and 124 are the channel regions 123 of the accesstransistors.

Alternatively, the doped regions 122, 124 and channel regions 123 may beformed using a single selective epitaxial process, rather the twoselective epitaxial processes used in the illustrated embodiment ofFIGS. 7-9. For example, in one such alternative embodiment a selectiveepitaxial process is performed within the openings 2310 of the structureof FIG. 6 to form doped pillars filling the openings 2310, the dopedpillars and having a first conductivity type. Next, dopants areimplanted within the doped pillars to form the channel regions having asecond conductivity type opposite the first conductivity type, and formthe second terminals on the channel regions and having the firstconductivity type. The portions of the doped pillars underlying thechannel regions are the first terminals.

Referring back to the structure illustrated in FIG. 9, next a portion ofdielectric 2300 is removed to expose outer surfaces of the doped regions122, 123, 124 and dielectric 2700 is grown on the exposed outersurfaces, resulting in the structure illustrated in the cross-sectionalview of FIG. 10.

Word line material, for example polysilicon, is then deposited on thestructure illustrated in FIG. 10, and planarized to expose a top surfaceof doped regions 124. The word line material is then patterned and asilicide process is performed to form conductive caps 127 on the dopedregions 124 and conductive layers on the tops of the word lines,resulting in the structure illustrated in the cross-sectional and topviews of FIGS. 11A and 11B. The conductive cap 127 and conductive layerson the tops of the word lines comprise a silicide containing, forexample, Ti, W, Co, Ni, or Ta. In one embodiment they comprise cobaltsilicide (CoSi) and are formed by depositing cobalt and performing arapid thermal process (RTP) such that the cobalt reacts with the siliconof the doped regions 124 to form the conductive caps 127 and reacts withthe word line material to form the conductive layers. It is understoodthat other silicides may also be formed in this manner by depositingtitanium, arsenic, doped nickel, or alloys thereof, in a manner similarto the example described herein using cobalt.

Next, a dielectric layer 270 is formed on the structure illustrated inFIGS. 11A-11B and openings having respective widths are formed throughthe dielectric layer to expose of a portion of the conductive caps 127.

The openings having a sublithographic widths can be formed, for example,by forming an isolation layer on the dielectric 270 and forming asacrificial layer on the isolation layer. Next, a mask having openingsclose to or equal to the minimum feature size of the process used tocreate the mask is formed on the sacrificial layer, the openingsoverlying the locations of the openings 1000. The isolation layer andthe sacrificial layer are then selectively etched using the mask,thereby forming vias in the isolation and sacrificial layers andexposing a top surface of the dielectric 270. After removal of the mask,a selective undercutting etch is performed on the vias such that theisolation layer is etched while leaving the sacrificial layer and thedielectric 270 intact. A fill material is then formed in the vias, whichdue to the selective undercutting etch process results in a self-alignedvoid in the fill material being formed within each via. Next, ananisotropic etching process is performed on the fill material to openthe voids, and etching continues until the dielectric 270 is exposed inthe region below the vias, thereby forming a sidewall spacer comprisingfill material within each via. The sidewall spacers have an openingdimension substantially determined by the dimensions of the voids, andthus can be less than the minimum feature size of a lithographicprocess. Next, the dielectric 270 is etched using the sidewall spacersas an etch mask, thereby forming openings having a widths less than theminimum lithographic feature size. The isolation layer and thesacrificial layer can be removed by a planarization process such as CMP.See, for example, U.S. Pat. No. 7,351,648 and U.S. patent applicationSer. No. 11/855,979, which are incorporated by reference herein.

Next, electrodes 250 are formed within the openings in the dielectriclayer 270 to contact the conductive caps 127. The electrodes 250 can beformed, for example, by depositing electrode material within theopenings in the dielectric layer 270 using Chemical Vapor Deposition,followed by a planarizing process such as CMP. In embodiments in whichthe openings are formed using an isolation layer and a sacrificial layeras described above, in alternative embodiments the electrode materialmay be deposited within the openings and overlying the isolation layerand the sacrificial layer. A subsequent planarization process such asCMP can then remove the isolation layer and the sacrificial layer.

Next, memory material 290 can be formed by blanket depositing a layer ofmemory material, and the conductive material 140 can be formed byblanket depositing one or more layers of conductive material 140overlying the memory material 290. Dielectric 1996 is then formed,contacts 1950, 1995, 1965 are formed, and conductive lines 1997 and 1960are formed, resulting in the structure illustrated in thecross-sectional views of FIGS. 2A-2B.

In an alternative embodiment, the step of forming the electrodes 250within the openings in the dielectric layer 270 discussed above isomitted. Instead, memory material 290 is formed on the structure andwithin the openings in the dielectric layer 270, and conductive material140 is formed on the memory material 290, resulting in the structureillustrated in FIGS. 2C-2D.

Since the logic devices in the periphery region and the memory cellshaving vertical channel access transistors in the memory region aremanufactured concurrently in the manufacturing steps described, thememory device has a reduced complexity and addresses design integrationissues of periphery and memory regions.

FIG. 12 is a simplified block diagram of an integrated circuit 2910including a memory array 2912 implemented using memory cells having amemory plane overlying vertical channel field effect transistor accessdevices as described herein. A memory plane termination circuit 2970 iscoupled to the array and provides a common voltage to the memory planeof the array 2912. A word line decoder 2914 having read, set and resetmodes is coupled to and in electrical communication with a plurality ofword lines 2916 arranged along rows in the memory array 2912. A bit line(column) decoder 2918 is in electrical communication with a plurality ofbit lines 2920 arranged along columns in the array 2912 for reading,setting, and resetting the phase change memory cells (not shown) inarray 2912. Addresses are supplied on bus 2922 to word line decoder anddrivers 2914 and bit line decoder 2918. Sense amplifiers and data-instructures in block 2924, including voltage and/or current sources forthe read, set, and reset modes are coupled to bit line decoder 2918 viadata bus 2926. Data is supplied via a data-in line 2928 frominput/output ports on integrated circuit 2910, or from other datasources internal or external to integrated circuit 2910, to data-instructures in block 2924. Other circuitry 2930 may be included onintegrated circuit 2910, such as a general purpose processor or specialpurpose application circuitry, or a combination of modules providingsystem-on-a-chip functionality supported by array 2912. Data is suppliedvia a data-out line 2932 from the sense amplifiers in block 2924 toinput/output ports on integrated circuit 2910, or to other datadestinations internal or external to integrated circuit 2910.

A controller 2934 implemented in this example, using a bias arrangementstate machine, controls the application of bias arrangement supplyvoltages and current sources 2936, such as read, program, erase, eraseverify and program verify voltages and/or currents. Controller 2934 maybe implemented using special-purpose logic circuitry as known in theart. In alternative embodiments, controller 2934 comprises ageneral-purpose processor, which may be implemented on the sameintegrated circuit to execute a computer program to control theoperations of the device. In yet other embodiments, a combination ofspecial-purpose logic circuitry and a general-purpose processor may beutilized for implementation of controller 2934.

FIG. 13 illustrates a schematic diagram of a portion of a memory cellarray 3000 implemented using memory cells having field effecttransistors with vertical channels and memory elements comprisingprogrammable resistance material, the transistors arranged in a commonsource configuration.

In a common source configuration, the source terminals of the memorycells are coupled to a common voltage, and the input and output are thegate and drain terminals respectively. Thus, in operation voltages andthe bit lines 120 and word lines 130 induce a current from the bit lines120 to the source terminals, or vice versa, through the drain terminals,channel regions, and memory elements.

In FIG. 13 the source terminals are coupled to ground. Alternatively,the source terminals may be coupled to a voltage source for applying acommon voltage other than ground.

Memory cell 3010 is representative of memory cells of array 3000 andcomprises field effect transistor 3015 and phase change memory element3025. The word line 130 b acts as the gate terminal of the transistor3015, and the second terminal acting as the drain of the accesstransistor 3015 is coupled to the bit line 120 b via the memory element3025.

Reading or writing to memory cells of the array 3000 can be achieved byapplying an appropriate voltage to the corresponding word line 130 andan appropriate voltage or current to the corresponding bit line 120 toinduce a current through the memory element. The level and duration ofthe voltages/currents applied is dependent upon the operation performed,e.g. a reading operation or a writing operation.

FIGS. 14A and 14B illustrate cross-sectional views of a portion of anembodiment of memory cells (including representative memory cell 3110)arranged in the array 3000, FIG. 14A taken along the word lines 130 andFIG. 14B taken along the bit lines 120.

In FIGS. 14A-14B the array 3000 includes memory region 3100 andperiphery region 1910 on the single-crystalline semiconductor substrate200.

The memory region 3100 includes common doped region 3110 underlying thefirst terminals 122 of the access transistors of the array 300 tocoupled the transistors in a common source configuration. The commondoped region 3100 has a conductivity type opposite that of the well 205,and in the illustrated embodiment comprises N-type doped material. Thecommon doped region 3110 is coupled to a common voltage, for example byan array of contacts (not shown).

As can be seen in FIGS. 14A and 14B, the programmable resistance memorymaterial on the electrodes 250 comprises strips 3150 of memory material.The bit lines 120 comprise conductive material on the strips 3150 ofmemory material. The memory elements of the array 3000 comprises aportion of a strip 3150 adjacent the corresponding electrodes 250. Forexample, memory element 3025 of memory cell 3010 comprises a portion ofthe strip 3150 b.

As can be seen in FIGS. 14A and 14B, the first terminals 122 of theaccess transistors in the memory region 3100 and the gate dielectriclayer 1993 are both on the substantially planar top surface 201 of thesubstrate. As described in more detail below with reference to FIGS. 15to 16, the logic device 1986 in the periphery region and the memorycells having vertical channels can be manufactured concurrently. As aresult, the memory device has a reduced complexity and addresses designintegration issues of periphery and memory regions, thereby reducing thecost.

In FIGS. 14A-14B the memory cells are implemented in a mushroom-typeconfiguration. Alternatively, other types of configurations can be used.In one alternative embodiment the electrodes 250 of the array of FIGS.14A-14B are omitted and the memory material of the strips 3150 extendwithin the opening in the dielectric 270 to contact the conductive cap127, resulting in a pore-type configuration like that shown in FIGS.2C-2D.

FIGS. 15 to 16 illustrate steps in a fabrication sequence suitable formanufacturing an array of memory cells illustrated in FIGS. 14A-14B.

Trench isolation structures 232 are formed in the well 205, gatedielectric layer 1993 is formed on the top surface 201 of the peripheryregion 1910 of the substrate 200, and gate structure 1987 is formed onthe gate dielectric layer 1993. The well 205, trench isolation structure232, gate dielectric layer 1987, and gate structure 1987 can be formed,for example, as described above with reference to FIGS. 3-4. Next,common doped region 3110 and doped regions 1988, 1989 are formed withinthe periphery region 1910, resulting in the structure illustrated in thecross-sectional view of FIG. 15. In the illustrated embodiment thecommon doped region 3110 and doped regions 1988, 1989 are formed by asingle ion implantation process, and thus are formed at the same time.

Next, the word lines 130, the first and second terminals 122, 124 andchannel regions 123 can be formed as discussed above with reference toFIGS. 6 to 11. Next, dielectric material 270 and electrodes 250 areformed, for example, as discussed above with reference to FIGS. 11A-11B.

Next, memory material layer 3300 is formed on the electrodes 250, andconductive bit line material 3310 is formed on the memory material layer3300, resulting in the structure illustrated in the cross-sectionalviews of FIGS. 16A-16B. The memory material layer 3300 and conductivebit line material 3310 are then patterned to form strips 3150 of memorymaterial and bit lines 120 on the strips. The strips 3150 and bit lines120 can be formed by forming a lithographic mask on the conductive bitline material 3310 and then etching the memory material layer 3300 andconductive bit line material 3310. Dielectric 1996 is then formed,contacts 1950, 1995, 1996 are formed, and conductive lines 1997 and 1960are formed, resulting in the structure illustrated in thecross-sectional views of FIGS. 14A-14B.

FIG. 17 is a simplified block diagram of an integrated circuit 3410including a memory array 3412 implemented using memory cells havingvertical channel field effect transistor access devices arranged in acommon source configuration as described herein. A word line decoder3414 having read, set and reset modes is coupled to and in electricalcommunication with a plurality of word lines 3416 arranged along rows inthe memory array 3412. A bit line (column) decoder 3418 is in electricalcommunication with a plurality of bit lines 3420 arranged along columnsin the array 3412 for reading, setting, and resetting the phase changememory cells (not shown) in array 3412. Addresses are supplied on bus3422 to word line decoder and drivers 3414 and bit line decoder 3418.Sense amplifiers and data-in structures in block 3424, including voltageand/or current sources for the read, set, and reset modes are coupled tobit line decoder 3418 via data bus 3426. Data is supplied via a data-inline 3428 from input/output ports on integrated circuit 3410, or fromother data sources internal or external to integrated circuit 3410, todata-in structures in block 3424. Other circuitry 3430 may be includedon integrated circuit 3410, such as a general purpose processor orspecial purpose application circuitry, or a combination of modulesproviding system-on-a-chip functionality supported by array 3412. Datais supplied via a data-out line 3432 from the sense amplifiers in block3424 to input/output ports on integrated circuit 3410, or to other datadestinations internal or external to integrated circuit 3410.

A controller 3434 implemented in this example, using a bias arrangementstate machine, controls the application of bias arrangement supplyvoltages and current sources 3436, such as read, program, erase, eraseverify and program verify voltages and/or currents. Controller 3434 maybe implemented using special-purpose logic circuitry as known in theart. In alternative embodiments, controller 3434 comprises ageneral-purpose processor, which may be implemented on the sameintegrated circuit to execute a computer program to control theoperations of the device. In yet other embodiments, a combination ofspecial-purpose logic circuitry and a general-purpose processor may beutilized for implementation of controller 3434.

While the present invention is disclosed by reference to the preferredembodiments and examples detailed above, it is to be understood thatthese examples are intended in an illustrative rather than in a limitingsense. It is contemplated that modifications and combinations willreadily occur to those skilled in the art, which modifications andcombinations will be within the spirit of the invention and the scope ofthe following claims.

1. A device comprising: a substrate; a first dielectric overlying thesubstrate; a field effect transistor comprising: a first terminalextending through the first dielectric to contact the substrate; asecond terminal overlying the first terminal and having a top surface; avertical channel region separating the first and second terminals; agate of the field effect transistor on the first dielectric and adjacentthe vertical channel region, the gate of the field effect transistorhaving a top surface that is co-planar with the top surface of thesecond terminal; and a second dielectric separating the gate of thesecond field effect transistor from the vertical channel region.
 2. Thedevice of claim 1, further comprising a memory element electricallycoupled to the second terminal of the field effect transistor and anelectrode electrically coupled to the second terminal of the fieldeffect transistor.
 3. The device of claim 2, the memory elementcomprising programmable resistance memory material.
 4. The device ofclaim 2, the memory element comprising a charge storage region.
 5. Thedevice of claim 2, the memory element comprising a capacitor.
 6. Thedevice of claim 1, wherein the second dielectric surrounds the verticalchannel region and the second terminal.
 7. The device of claim 1,wherein the thickness of the second dielectric surrounding the verticalchannel region is less than that surrounding the second terminal.
 8. Adevice, comprising: a first insulator on a substrate; a first terminal,a channel region, and a second terminal vertically arranged, the firstterminal contacting the substrate; a second insulator surrounding thechannel regions; and a conductive element on the first insulator andsurrounding the second insulator, the conductive element having a topsurface that is co-planar with the top surface of the second terminal.9. The device of claim 8, the conductive element comprising a gate. 10.The device of claim 8, the conductive element comprising a word line.11. The device of claim 8, wherein the thickness of the second insulatorsurrounding the vertical channel region is less than that surroundingthe second terminal.
 12. The device of claim 8, further comprising amemory element electrically coupled to the second terminal.
 13. Thedevice of claim 12, further comprising an electrode electrically coupledto the second terminal.
 14. The device of claim 12, the memory elementcomprising programmable resistance memory material.
 15. The device ofclaim 12, the memory element comprising a capacitor.
 16. A device,comprising: a first insulator on a substrate; a transistor having afirst terminal extending through the first insulator to contact thesubstrate, the transistor having a vertical channel region separatingfirst and second terminals and having a second insulator separating agate and the vertical channel region, the second insulator having athickness surrounding the vertical channel region less than surroundingthe second terminal.
 17. The device of claim 16, further comprising amemory element electrically coupled to the second terminal.
 18. Thedevice of claim 17, further comprising a conductor on the memoryelement.
 19. The device of claim 17, the memory element comprisingprogrammable resistance memory material.
 20. The device of claim 17, thememory element comprising a capacitor.